I have been writing general articles as well as on my blog for some time now. These days, I ma really looking to upgrade my exposure game. I pulled up a list of sites but want to know from others what their experience was or if the sites have a specific demographic. Here's who I've been working with for about 3 yrs for my content and blog !
Delicious
Technorati
Article Income
Yahoo Bookmarks
Google Bookmarks
and I've been using Digg for about a year

If you want to get high quality backlink you should find high pr Social Bookmarking Sites. It can improve your search engine ranking. i got a source where you can find the list of social bookmarking sites (http://mizmizi.com/social-bookmarking-sites-list-2015-high-pr/)
and you will know how it is important for seo.